The present invention relates generally to a device and process for piecing on an open-end rotor spinning device, and more specifically on an open-end rotor spinning device with a spinning rotor which is installed in a housing in which negative pressure is applied during the spinning process, whereby fiber feeding is switched on in preparation of the piecing process, but the individual fibers are prevented from being deposited in the fiber collection groove of the spinning rotor and are evacuated by negative pressure until, in synchronization with the back-feeding of the yarn, the fiber evacuation is completed, the fibers are conveyed back into the fiber collection groove to be incorporated into a yarn end being fed back into the spinning rotor, and the drawing off of the yarn is resumed.
In a known process of this type, the fibers to be evacuated are taken in the housing of the opener device over the inlet opening of the fiber feeding channel to a suction channel through which the fibers are evacuated. The evacuation thus prevents deposition of fibers on the fiber collection surface (i.e. in the fiber groove of the spinning rotor) (WO 86/01235 A1). This procedure has the advantage that no openings occur in the fiber conveying path other than those already provided--e.g. a dirt collection opening. Such procedure has the disadvantage, however, that a space and material consuming fiber evacuation and control device is required.
In DE 25 05 943 a process for the preparation of the piecing process is shown. After braking the rotor the feed roller, by means of which fibers of a fiber sliver are conveyed to an opener roller, is caused to rotate for a brief time in order to feed a fiber strand end to the rotor. The fibers in this fiber strand end are removed, together with dust and dirt, by an air stream, whereupon the rotor is again driven. The feed roller then delivers a fiber strand end suitable for piecing via the opener roller into the rotor. In this known process the fibers are constantly guided into the rotor and must be removed again therefrom before the piecing process begins, or the rotor must be cleaned. Because the rotor must stop for fiber removal, the entire piecing process is lengthened.
DE 31 04 444 A1 describes a process in which fibers are prevented from entering the rotor. The fibers are guided along the circumference of the opener roller past the fiber feeding channel and are conveyed into an evacuation channel. Costly design is a disadvantage of this device.
In DE 34 41 677 C3 the fiber stream at the opener roller is also prevented from entering the fiber feeding channel. During piecing a switch-over between the evacuation point and the fiber feeding channel takes place in order to bring the fibers into contact with the introduced yarn end. The switching requires a certain amount of lead time in order to have the fiber stream present in the rotor at the right point in time. This control is relatively expensive.